Visualization of lysosomal membrane proteins by cryo electron tomography.

Lysosomes are essential organelles for cellular homeostasis and signaling, with dysfunction linked to neurological disorders, lysosomal storage diseases, and cancer. While proteomics has advanced our understanding of lysosomal composition, the structural characterization of lysosomal membrane proteins in their native environment remains a significant challenge. Here, we developed a cryo electron tomography workflow to visualize lysosomal membrane proteins within intact, native lysosomal membranes. We isolated endolysosomes by independently targeting two lysosomal membrane proteins, transient receptor potential mucolipin 1 and transmembrane protein 192, enriching organelles that exhibited the expected morphology and proteomic composition of the endolysosomal system. Sub-tomogram averaging enabled the structural refinement of key membrane and membrane-associated proteins, including V-ATPase, Flotillin, and Clathrin, directly within the lysosomal membrane, revealing their heterogeneous distribution across endolysosomal organelles. By integrating proteomics with structural biology, our workflow establishes a powerful platform for studying lysosomal membrane protein function in health and disease, paving the way for future discoveries in membrane-associated lysosomal mechanisms.